Example Leq and Lmax: Leq and Lmax Concepts

Figure 1

As the train approaches, the sound level rises from 52 dBA to 85dBA for six seconds before dropping to about 43 dBA at the 40thsecond. The sound level then rises sharply and quickly to 77dBA as the truck passes by before dropping down to 43 dBA. The equivalent sound level over 60 seconds is 75 dBA. The maximum sound level is 85 dBA.

Figure 2

The first graph illustrates a steady sound of 78dBA over 22 seconds. The second graph illustrates a steady sound of 67 dBA for five seconds followed by an absence of sound then by a steady sound of 78dBA for six seconds. This is followed by no sound for a few seconds and finally a steady sound of 71 dBA for five seconds. In the third graph, the sound rises steadily from 40 to 88dBA over seven seconds, decreases to 66 dBA before fluctuating slightly for 11 seconds and finally decreasing quickly to 23 dBA. In the fourth graph, sound rises sharply in a few seconds from troughs of 40 or 45 dBA to peaks of over 80 dBA before decreasing just as quickly to 40 or 45 dBA. This occurs six times.

A Typical Time History of Impulsive Sound Signals

Figure 3

The ambient sound fluctuates between 60 and 70 dBA over 100 seconds. The equivalent ambient sound level is 66 dBA. The general sound level from the noise source being measured is eight to ten dBA lower the ambient sound level. However, at eight times during this 100 seconds period, sharp impulse sounds rise well above the ambient sound level to 80 dBA or more.

Overview of the Procedures for Sound Level Determination

Figure 4

This figure contains the titles of the three different procedures for sound level determination described in this document. Method A is a simplified noise estimation procedure, method B is an assessment by prediction models, and method C combines assessment by field measurements and prediction models.

Control Point Measurement Procedure

Figure 5

Example Graph of Control Point Measurement Results

Figure 6

The Lmax near the crossing fluctuates sharply every few seconds between 77 and 87 dBA from the 24th to the 63rd second. The Leq near the crossing fluctuates in a similar pattern to the Lmax and during the same time interval but at a level between 70 and 76 dBA. The Lmax without rail crossing fluctuates between 60 and 66 dBA, but from the 30th to the 68th second. The Leq without rail crossing fluctuates 50 and 56 dBA also from the 30th to the 68th second.